Dehydration of Secondary Alcohols via Thermolysis of In Situ Generated Alkyl Diphenyl Phosphates: An Inexpensive and Environmentally Compatible Method for the Preparation of Alkenes
作者:Helmut Quast、Thomas Dietz
DOI:10.1055/s-1995-4084
日期:1995.10
Secondary alcohols are converted into diphenyl phosphate esters by the action of triphenyl phosphate or diphenyl phosphorochloridate in high-boiling, water-miscible solvents in the presence of base. The alkyl diphenyl phosphates undergo thermolysis to afford high yields of alkenes which distill from the reaction mixtures. Purification of the products is achieved by extraction with dilute sulfuric acid which removes traces of solvent and base that may have codistilled. The ratios of 2- (14) and 3-menthene (15), obtained from menthol (13) and neomenthol (16), and the formation of rear-ranged alkenes by 1,2-shifts from 3, 6, and 3,3-dimethylbutan-2-ol are consistent with ionic intermediates of the elimination reaction. The novel dehydration method offers distinct and important advantages over the existing methods.
仲醇在碱存在下,通过磷酸三苯酯或磷酸二苯酯在高沸点水溶性溶剂中的作用,转化为磷酸二苯酯。烷基二苯基磷酸酯经过热分解后,可得到高产率的烯烃,烯烃从反应混合物中蒸馏出来。用稀硫酸萃取可去除可能串蒸的微量溶剂和碱,从而提纯产物。从薄荷醇 (13) 和新薄荷醇 (16) 中得到的 2- (14) 和 3- 门特烯 (15) 的比例,以及从 3、6 和 3,3-二甲基丁-2-醇中通过 1,2 移位形成的后排烯,都与消除反应的离子中间体一致。与现有方法相比,这种新型脱水方法具有明显而重要的优势。